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Full-Text Articles in Physics

A Second-Order Realizable Scheme For Moment Advection On Unstructured Grids, Alberto Passalacqua, Frédérique Laurent, Rodney O. Fox Oct 2019

A Second-Order Realizable Scheme For Moment Advection On Unstructured Grids, Alberto Passalacqua, Frédérique Laurent, Rodney O. Fox

Chemical and Biological Engineering Publications

The second-order realizable 𝜁 moment advection scheme developed in Laurent and Nguyen (2017) is extended to the case of unstructured grids with cells of arbitrary shape. The necessary modifications to the scheme and the conditions under which the scheme ensures the realizability of the advected moment set are presented. The implementation of the scheme in the OpenFOAM® CFD toolbox is verified comparing the results obtained in one-dimensional test cases involving moment sets well inside the moment space, and at the boundary of the moment space. Results obtained with the proposed scheme are compared to the corresponding analytical solution. The scheme ...


A Quadrature-Based Moment Method For Polydisperse Bubbly Flows, Jeffrey C. Heylmun, Bo Kong, Alberto Passalacqua, Rodney O. Fox Jun 2019

A Quadrature-Based Moment Method For Polydisperse Bubbly Flows, Jeffrey C. Heylmun, Bo Kong, Alberto Passalacqua, Rodney O. Fox

Chemical and Biological Engineering Publications

A computational algorithm for polydisperse bubbly flow is developed by combining quadrature-based moment methods (QBMM) with an existing two-fluid solver for gas–liquid flows. Care is taken to ensure that the two-fluid model equations are hyperbolic by generalizing the kinetic model for the bubble phase proposed by Bieseuvel and Gorissen (1990). The kinetic formulation for the bubble phase includes the full suite of interphase momentum exchange terms for bubbly flow, as well as ad hoc bubble–bubble interaction terms to model the transition from isolated bubbles to regions of pure air at very high bubble-phase volume fractions. A robust numerical ...


Effect Of (Poly)Electrolytes On The Interfacial Assembly Of Peg Functionalized Gold Nanoparticles, Srikanth Nayak, Max Fieg, Wenjie Wang, Wei Bu, Surya Mallapragada, David Vaknin Jan 2019

Effect Of (Poly)Electrolytes On The Interfacial Assembly Of Peg Functionalized Gold Nanoparticles, Srikanth Nayak, Max Fieg, Wenjie Wang, Wei Bu, Surya Mallapragada, David Vaknin

Chemical and Biological Engineering Publications

We report on the effect of interpolymer complexes (IPCs) of poly(acrylic acid) (PAA) with poly(ethylene glycol) functionalized Au nanoparticles (PEG-AuNPs) as they assemble at the vapor-liquid interface, using surface sensitive synchrotron X-ray scattering techniques. Depending on the suspension pH, PAA functions both as a weak polyelectrolyte and a hydrogen bond donor, and these two roles affect the interfacial assembly of PEG-AuNPs differently. Above its isoelectric point, we find that PAA leads to the formation of a PEG-AuNPs monolayer at the interface with hexagonal structure. In the presence of high concentration of HCl (i.e., below the isoelectric point ...


An Open-Source Quadrature-Based Population Balance Solver For Openfoam, Alberto Passalacqua, Frédérique Laurent, Ehsan Madadi-Kandjani, Jeffrey C. Heylmun, Rodney O. Fox Feb 2018

An Open-Source Quadrature-Based Population Balance Solver For Openfoam, Alberto Passalacqua, Frédérique Laurent, Ehsan Madadi-Kandjani, Jeffrey C. Heylmun, Rodney O. Fox

Chemical and Biological Engineering Publications

The extended quadrature method of moments (EQMOM) for the solution of population balance equations (PBE) is implemented in the open-source computational fluid dynamic (CFD) toolbox OpenFOAM as part of the OpenQBMM project. The moment inversion procedure was designed (Nguyen et al., 2016) to maximize the number of conserved moments in the transported moment set. The algorithm is implemented in a general structure to allow the addition of other kernel density functions defined on R+, and arbitrary kernels to describe physical phenomena involved in the evolution of the number density function. The implementation is verified with a set of zero-dimensional cases ...


Interpolymer Complexation As A Strategy For Nanoparticle Assembly And Crystallization, Srikanth Nayak, Nathan Horst, Honghu Zhang, Wenjie Wang, Surya Mallapragada, Alex Travesset, David Vaknin Jan 2018

Interpolymer Complexation As A Strategy For Nanoparticle Assembly And Crystallization, Srikanth Nayak, Nathan Horst, Honghu Zhang, Wenjie Wang, Surya Mallapragada, Alex Travesset, David Vaknin

Chemical and Biological Engineering Publications

Controlled self-assembly of nanoparticles into ordered structures is a major step in fabricating nanotechnology based devices. Here, we report on the self-assembly of high quality superlattices of nanoparticles in aqueous suspensions induced via interpolymer complexation. Using small angle X-ray scattering, we demonstrate that the NPs crystallize into superlattices of FCC symmetry, initially driven by hydrogen bonding and subsequently by van der Waals forces between the complexed coronas of hydrogen-bonded polymers. We show that the lattice constant and crystal quality can be tuned by polymer concentration, suspension pH and the length of polymer chains. Interpolymer complexation to assemble nanoparticles is scalable ...


Application Of The Fokker-Planck Molecular Mixing Model To Turbulent Scalar Mixing Using Moment Methods, Ehsan Madadi-Kandjani, Rodney O. Fox, Alberto Passalacqua Jun 2017

Application Of The Fokker-Planck Molecular Mixing Model To Turbulent Scalar Mixing Using Moment Methods, Ehsan Madadi-Kandjani, Rodney O. Fox, Alberto Passalacqua

Chemical and Biological Engineering Publications

An extended quadrature method of moments using the beta kernel density function (beta-EQMOM) is used to approximate solutions to the evolution equation for univariate and bivariate composition probability distribution functions (PDFs) of a passive scalar for binary and ternary mixing. The key element of interest is the molecular mixing term, which is described using the Fokker-Planck (FP) molecular mixing model. The direct numerical simulations (DNSs) of Eswaran and Pope ["Direct numerical simulations of the turbulent mixing of a passive scalar,"Phys. Fluids 31, 506 (1988)] and the amplitude mapping closure (AMC) of Pope ["Mapping closures for turbulent mixing and reaction ...


Morphological Transformations In The Magnetite Biomineralizing Protein Mms6 In Iron Solutions: A Small-Angle X‑Ray Scattering Study, Honghu Zhang, Xunpei Liu, Shuren Feng, Wenjie Wang, Klaus Schmidt-Rohr, Mufit Akinc, Marit Nilsen-Hamilton, David Vaknin, Surya K. Mallapragada Feb 2015

Morphological Transformations In The Magnetite Biomineralizing Protein Mms6 In Iron Solutions: A Small-Angle X‑Ray Scattering Study, Honghu Zhang, Xunpei Liu, Shuren Feng, Wenjie Wang, Klaus Schmidt-Rohr, Mufit Akinc, Marit Nilsen-Hamilton, David Vaknin, Surya K. Mallapragada

Chemical and Biological Engineering Publications

Magnetotactic bacteria that produce magnetic nanocrystals of uniform size and well-defined morphologies have inspired the use of biomineralization protein Mms6 to promote formation of uniform magnetic nanocrystals in vitro. Small angle X-ray scattering (SAXS) studies in physiological solutions reveal that Mms6 forms compact globular threedimensional (3D) micelles (approximately 10 nm in diameter) that are, to a large extent, independent of concentration. In the presence of iron ions in the solutions, the general micellar morphology is preserved, however, with associations among micelles that are induced by iron ions. Compared with Mms6, the m2Mms6 mutant (with the sequence of hydroxyl/carboxyl containing ...


Characterization Of Sheared Colloidal Aggregation Using Langevin Dynamics Simulation, Sergiy Markutsya, Rodney O. Fox, Shankar Subramaniam Jun 2014

Characterization Of Sheared Colloidal Aggregation Using Langevin Dynamics Simulation, Sergiy Markutsya, Rodney O. Fox, Shankar Subramaniam

Chemical and Biological Engineering Publications

Aggregation of colloidal particles under shear is studied in model systems using a Langevin dynamics model with an improved interparticle interaction potential. In the absence of shear, aggregates that form are characterized by compact structure at small scales and ramified structure at larger scales. This confirms the structural crossover mechanism previously suggested by Sorensen and coworkers, that colloidal aggregation occurs due to monomer addition at small scales and due to cluster-cluster aggregation at large scales. The fractal dimension of nonsheared aggregates is scale-dependent. Smaller aggregates have a higher fractal dimension than larger ones, but the radius of gyration where this ...


Self-Assembly And Biphasic Iron-Binding Characteristics Of Mms6, A Bacterial Protein That Promotes The Formation Of Superparamagnetic Magnetite Nanoparticles Of Uniform Size And Shape, Lijun Wang, Tanya Prozorov, Pierre E. Palo, Xunpei Liu, David Vaknin, Ruslan Prozorov, Surya K. Mallapragada, Marit Nilsen-Hamilton Jan 2012

Self-Assembly And Biphasic Iron-Binding Characteristics Of Mms6, A Bacterial Protein That Promotes The Formation Of Superparamagnetic Magnetite Nanoparticles Of Uniform Size And Shape, Lijun Wang, Tanya Prozorov, Pierre E. Palo, Xunpei Liu, David Vaknin, Ruslan Prozorov, Surya K. Mallapragada, Marit Nilsen-Hamilton

Chemical and Biological Engineering Publications

Highly ordered mineralized structures created by living organisms are often hierarchical in structure with fundamental structural elements at nanometer scales. Proteins have been found responsible for forming many of these structures, but the mechanisms by which these biomineralization proteins function are generally poorly understood. To better understand its role in biomineralization, the magnetotactic bacterial protein, Mms6, which promotes the formation in vitro of superparamagnetic magnetite nanoparticles of uniform size and shape, was studied for its structure and function. Mms6 is shown to have two phases of iron binding: one high affinity and stoichiometric and the other low affinity, high capacity ...


Interfacial Properties And Iron Binding To Bacterial Proteins That Promote The Growth Of Magnetite Nanocrystals: X-Ray Reflectivity And Surface Spectroscopy Studies, Wenjie Wang, Wei Bu, Lijun Wang, Pierre E. Palo, Surya K. Mallapragada, Marit Nilsen-Hamilton, David Vaknin Jan 2012

Interfacial Properties And Iron Binding To Bacterial Proteins That Promote The Growth Of Magnetite Nanocrystals: X-Ray Reflectivity And Surface Spectroscopy Studies, Wenjie Wang, Wei Bu, Lijun Wang, Pierre E. Palo, Surya K. Mallapragada, Marit Nilsen-Hamilton, David Vaknin

Chemical and Biological Engineering Publications

Surface sensitive X-ray scattering and spectroscopic studies have been conducted to determine structural properties of Mms6, the protein in Magnetospirillum magneticum AMB-1 that is implicated as promoter of magnetite nanocrystals growth. Surface pressure versus molecular area isotherms indicate Mms6 forms stable monolayers at the aqueous/vapor interface that are strongly affected by ionic conditions of the subphase. Analysis of X-ray reflectivity from the monolayers shows that the protein conformation at the interface depends on surface pressure and on the presence of ions in the solutions, in particular of iron ions and its complexes. X-ray fluorescence at grazing angles of incidence ...


Dendrimer-Fullerenol Soft-Condensed Nanoassembly, Priyanka Bhattacharya, Seung Ha Kim, Pengyu Chen, Ran Chen, Anne M. Spuches, Jared M. Brown, Monica H. Lamm, Pu Chun Ke Jan 2012

Dendrimer-Fullerenol Soft-Condensed Nanoassembly, Priyanka Bhattacharya, Seung Ha Kim, Pengyu Chen, Ran Chen, Anne M. Spuches, Jared M. Brown, Monica H. Lamm, Pu Chun Ke

Chemical and Biological Engineering Publications

Nanoscale assembly is an area of research that has vast implications for molecular design, sensing, nanofabrication, supramolecular chemistry, catalysis, and environmental remediation. Here we show that poly(amidoamine) (PAMAM) dendrimers of both generations 1 (G1) and 4 (G4) can host 1 fullerenol per 2 dendrimer primary amines as evidenced by isothermal titration calorimetry, dynamic light scattering, and spectrofluorometry. Thermodynamically, the interactions were similarly spontaneous between both generations of dendrimers and fullerenols, however, G4 formed stronger complexes with fullerenols resulting from their higher surface charge density and more internal voids, as demonstrated by spectrofluorometry. In addition to hydrogen bonding that existed ...


Single-Molecule Dendrimer-Hydrocarbon Interaction, Karthikeyan Pasupathy, Nicholas W. Suek, John L. Lyons, Justin Ching, Aaron Jones, Qi Lu, Monica H. Lamm, Pu Chun Ke Jan 2008

Single-Molecule Dendrimer-Hydrocarbon Interaction, Karthikeyan Pasupathy, Nicholas W. Suek, John L. Lyons, Justin Ching, Aaron Jones, Qi Lu, Monica H. Lamm, Pu Chun Ke

Chemical and Biological Engineering Publications

We report our single-molecule fluorescence microscopy and molecular dynamics simulation studies on the interaction of poly(amidoamine) dendrimer and squalane hydrocarbon in aqueous solution. Our spectrophotometry measurements indicate that this interaction increases with the pH of the solvent. Our simulations show that squalane resides primarily on the perimeter of the dendrimer at low to neutral pH, but becomes encapsulated by the dendrimer at high pH. Using single-molecule fluorescence microscopy, we have identified that the binding between PAMAM and squalane is reversible. At a pH value of 8, the approaching, binding, and characteristic times of a single fluorescently-labeled dendrimer to squalane ...


Nanoparticle Ordering Via Functionalized Block Copolymers In Solution, Rastko Sknepnek, Joshua A. Anderson, Monica H. Lamm, Jorg Schmalian, Alex Travesset Jan 2008

Nanoparticle Ordering Via Functionalized Block Copolymers In Solution, Rastko Sknepnek, Joshua A. Anderson, Monica H. Lamm, Jorg Schmalian, Alex Travesset

Chemical and Biological Engineering Publications

We consider nanoparticles and functionalized copolymers, block copolymers with attached end groups possessing a specific affinity for nanoparticles, in solution. Using molecular dynamics, we show that nanoparticles are able to direct the self-assembly of the polymer/ nanoparticle composite. We perform a detailed study for a wide range of nanoparticle sizes and concentrations. We show that the nanoparticles order in a number of distinct phases: simple cubic, layered hexagonal, hexagonal columnar, gyroid, and a novel square columnar. Our results show that nanoparticles ordered with functionalized block copolymers can provide a simple and efficient tool for assembling novel materials with nanometer scale ...


Magnetic Irreversibility And The Verwey Transition In Nanocrystalline Bacterial Magnetite, Ruslan Prozorov, Tanya Prozorov, Surya K. Mallapragada, Balaji Narasimhan, Timothy J. Williams, Dennis A. Bazylinski Jan 2007

Magnetic Irreversibility And The Verwey Transition In Nanocrystalline Bacterial Magnetite, Ruslan Prozorov, Tanya Prozorov, Surya K. Mallapragada, Balaji Narasimhan, Timothy J. Williams, Dennis A. Bazylinski

Chemical and Biological Engineering Publications

The magnetic properties of biologically produced magnetite nanocrystals biomineralized by four different magnetotactic bacteria were compared to those of synthetic magnetite nanocrystals and large, high-quality single crystals. The magnetic feature at the Verwey temperature TV was clearly seen in all nanocrystals, although its sharpness depended on the shape of individual nanoparticles and whether or not the particles were arranged in magnetosome chains. The transition was broader in the individual superparamagnetic nanoparticles for which TB < TV, where TB is the superparamagnetic blocking temperature. For nanocrystals organized in chains, the effective blocking temperature TB > TV and the Verwey transition is sharply defined. No correlation between particle size and TV was found. Furthermore, measurements of M (H,T,time) suggest that ...